<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .triangle1 {
            width: 0px;
            border: 100px solid transparent;
            border-bottom: 100px solid blue;
        }
        
        .triangle2 {
            width: 200px;
            height: 200px;
            background-color: red;
            clip-path: polygon(0% 0%, 100% 0%, 50% 50%);
        }
    </style>
</head>

<body>
    <div class="triangle1"></div><br>
    <div class="triangle2"></div>
</body>

</html>